WASHINGTON — Republicans have elected South Dakota Sen. John Thune as the next Senate majority leader, completing a momentous shift in their leadership that elevates a top deputy of Sen. Mitch McConnell into a key position as President-elect Donald Trump returns to the White House. [time-brightcove not-tgx=”true”] Thune, who is 63 and in his fourth Senate term, has promised to work closely with Trump despite differences the two have had over the years.